1. Field of the Invention
The present invention relates to a liquid discharging apparatus having a circulating flow path.
2. Description of the Related Art
A head of a liquid discharging apparatus is known, which utilizes a piezo-electric element (PZT) or a heater (heating element) as an energy generating element, which generates energy for discharging a liquid. When such a liquid discharging apparatus is left for a long period of time without liquid discharge, a liquid in the vicinity of a discharge port dries, increases in viscosity, or solidifies to cause clogging of the discharge port, adversely affecting the discharge of droplets.
A cap mechanism is known for sealing the discharge port face with a cap to prevent the liquid in the vicinity of the discharge port from drying. However, such a conventional cap mechanism has its limits in preventing clogging of the discharge port by the dryness of the liquid at a position where it contacts the atmosphere in the vicinity of the exit of the discharge port.
Japanese Patent Application Laid-Open No. 2006-88575 and U.S. Pat. No. 4,937,598 discusses a circulating flow path having a discharge port midway thereof and in which a liquid flows from the upstream side to the downstream side, and in which liquid circulation in the flow path prevents the liquid in the vicinity of the discharge port from drying.
However, the techniques discussed in Japanese Patent Application Laid-Open No. 2006-88575 and U.S. Pat. No. 4,937,598 assume only one direction of liquid flow, and the liquid on the downstream side of the energy generating element further flows only toward the downstream side. Therefore, the techniques have a large energy loss because the liquid is circulated so as to overcome the refill by a capillary force from the downstream side of the energy generating element after liquid discharge.
If air bubbles or dust enters the flow path, sending the liquid at such a very high flow velocity in this way may remarkably vary the flow velocity, and largely fluctuate the pressure at the discharge port. There has been a concern that this phenomenon adversely affects the discharge performance. There has been another concern that supplying the liquid only from one direction to the energy generating element may cause an offset in discharging direction, resulting in image quality degradation by deviation between impact positions of the main droplet and the sub droplet following the main droplet.